The present invention relates to a slider for double-cylinder circular knitting machines, particularly for hosiery knitting.
It is known that double-cylinder circular hosiery knitting machines generally comprise a lower needle cylinder and an upper needle cylinder which are mutually coaxial and can be actuated rigidly together with a rotary motion about their common axis.
In the skirt or curved surface of the lower needle cylinder and in the skirt or curved surface of the upper needle cylinder a plurality of axial slots are provided. The axial slots of the upper needle cylinder are aligned with the slots formed in the curved surface of the lower needle cylinder. Each one of the axial slots of the lower needle cylinder generally accommodates, starting from below, a selector and a slider, whereas each one of the axial slots of the upper needle cylinder accommodates a slider. Between the two needle cylinders, i.e., in the knitting region, in each one of the axial slots there is a needle which has two tips, respectively an upper tip and a lower tip; depending on whether plain stitches or purl stitches are to be produced, said needle is moved into the lower needle cylinder so that it knits with its upper tip or into the lower needle cylinder so that it knits with its lower tip.
Since the needle does not have a heel, it is actuated by means of the slider located in the lower needle cylinder or by means of the slider arranged in the upper needle cylinder depending on whether it is meant to form plain or purl stitches.
The sliders currently used in double-cylinder circular hosiery knitting machines are generally constituted by an elongated laminar body which has a first longitudinal side which is meant to rest on the bottom of the axial slot formed in the curved surface of the lower needle cylinder or in the curved surface of the upper needle cylinder.
Said sliders are further provided with two heels which are mutually spaced along the longitudinal extension of the slider and protrude transversely from a second longitudinal side of the slider which lies opposite the first side.
Said heels are used to move the slider along the corresponding axial slot of the lower needle cylinder or upper needle cylinder, so as to produce the actuation of the needle that is associated with said slider in the various knitting processes of the machine.
The slider furthermore has on its first longitudinal side, i.e., on its side directed toward the bottom of the axial slot inside which it is accommodated, a hook which engages the lower or upper tip of the needle, depending on whether the slider is in the lower needle cylinder or in the upper needle cylinder.
A plurality of cams are arranged around the curved surface of the lower needle cylinder and around the curved surface of the upper needle cylinder and form a series of paths with which the heels of the sliders engage when the needle cylinders are actuated so as to rotate about their axis with respect to said cams. The paths formed by the cams are shaped so as to produce the movement of the sliders along the axial slots of the needle cylinders in which they are accommodated and accordingly produce the actuation of the needles associated therewith.
In currently commercially available double-cylinder circular hosiery knitting machines, many of the cams that determine the paths for the heels of the sliders are provided so that they can move in a radial direction with respect to the needle cylinders, so that they can be transferred from an active position, in which they are close to the needle cylinders so that they can be engaged by the heels of the sliders, to an inactive position, in which they are spaced from the needle cylinders so as to avoid interfering with the heels of the sliders, or viceversa, so as to allow to produce different kinds of knitting.
The presence of these movable cams, which is required in order to perform the different kinds of knitting, entails the problem that it considerably increases the complexity of the structure of the entire machine.
Furthermore, the presence of these movable cams forces the provision, on board the machine, of a specific actuation program which intervenes if an accidental stoppage of the machine occurs due to a power failure; said program restores the correct position of the movable cams before knitting resumes, because if the machine were to restart without first restoring the correct position of the movable cams, the heels of the sliders might break.
In practice, the presence of these movable cams makes it necessary to provide the machine with electronic programs which store the position of the movable cams when the power failure occurred, and this constitutes a further complication in the execution of the machine.